Chair mat



FIG. 1 is a front view of the chair mat.

FIG. 2 is a back view of the claimed design.

FIG. 3 is a side view of the claimed design; and,

FIG. 4 is a bottom view of the claimed design.

The broken lines in FIG. 1 represent environmental matter, which forms no part of the claimed design. 

CLAIM I claim the ornamental design for a chair mat, as shown and described. 